Manufacture of hydrogen fluoride



May 16, 1950 E. a. LoPKr-:R ETAL MANUFACTURE OF' HYDROGEN FLUORIDE Filed March 14, 1946 INVENTORS .JT f'. PEV/P55 5 ff- @Pfff/e B ATTORNEY Patented May 16, 1950 TENT OFFICE MANUFACTURE OF HYDROGEN FLUORIDE Edwin B. Lopker, Oaklyn, and John E. Peirce, Arlington, N. J., assignors to Allied Chemical & Dye Corporation, a corporation of New York Application March 14, 1946, Serial No. 654,456

2 Claims.

This invention relates to the manufacture of hydrogen fluoride.

In general, prior processes for making anhydrous liquid HF are such as to require use of substantial quantities of extraneous refrigerating agent or a fractional distillation step. This invention aims to provide a process which does not embody either of these features and which, in a practical sense, is self-refrigerating.

The invention, its objects and advantages ap pear from the following Vdescription taken in connection with the accompanying drawing diagrammatically showing one form of apparatus in which the process of this invention may be carried out.

Referring to the drawing, I indicates a conventional furnace in which i'luorspar and sulfuric acid are reacted in the usual way to form a crude HF gas containing, for example, by weight 70 or more HF, 2 SiF4, some sulfuric acid mist, and air. The furnace gas, usually at temperatures of 105 to 115 C., is introduced into the bottom of a packed tower Il, and contacted therein countercurrent with strong sulfuric acid which is recirculated by means of the apparatus including a sulfuric acid discharge pipe I2, sump tank III, pump I5, cooler I6 and return pipe I8 thru which acid may be sprayed into the top of the tower thru a suitable distributor. The purpose of tower II is to dry the gas and remove solid impurities. The liquor circulating system is operated so that the sulfuric acid fed into the top of the tower is at temperature of not less than Sil-90 C., such temperature being maintained so as to minimize absorption of I-lIF out of the gas stream. In order to effect efficient drying, the HzSOv. content of the liquor in tower is kept high, and usually the liquor fed in thru pipe I8 contains about 88.2% HzSOi, 1.8% water and 10% absorbed I-llF. Liquid discharged into the sump tank thru pipe I2 ordinarily contains about 87.3% HzSO-i, 2.7% H2O, and 10% absorbed I-IF. To keep the H2SO4 strength of the circulating liquor at the desired relatively high concentration, S03, preferably in the form of oleum, is fed into the circulating system thru pipe 22 in quantity such as to form about 97% H2504 with all of the water vapor entering from furnace I0.

Drying tower exit gas flows thru Vconduit 23 into a separator 24 which may be of any suitable type to effect substantially complete separation from the gas stream of any entrained sulfuric acid mist. In the practice of this invention, the crude HF generating process and apparatus units so far described are carried out and designed so as to form in separator exit pipe 26 a gas which contains by weight not less than HF, not more than 0.5% H2O and substantially no sulfuric acid mist. Ordinarily, the Iwater content of this gas is preferably not more than 0.1% by weight.

The incoming gas stream, which now may be at temperature of 70-75 C., passes thru a control valve 30 and pipe section 3| to the suction side of a compressor 33. The latter is preferably of the turbine or screw type in which construction is such that no contact between the HF gas and lubricant is permitted. In pipe section 3|, the incoming HF gas is mixed with recycled anhydro-us HF vapor which is formed in a subsequent step in the process.

In accordance with this invention, the HF content of the incoming gas is substantially completely liquefied without the use of extraneous refrigerating agent. To this end, the combined gas stream in pipe 3| is rst compressed to a substantial superatmospheric pressure. While extent of compression may vary over a relatively Wide range, depending upon the particular conditions, ordinarily the gas is compressed to a pressure of not less than 20 lbs. gauge and pressure may be as high as 70 lbs. gauge. In the compression step, a substantial amount of heat is generated.' The hot gas stream is subjected to a preliminary cooling operation in which enough heat is removed from the gas to effect liquefaction of a substantial quantity of HF. Such cooling operation may be stepwise and involve passage of the compressed gas thru several coolers connected in series, or this preliminary cooling may be effected in a single step as exempliiled herein. Thus, the gas stream is passed thru pipe 34 into a cooling zone 35 surrounded throughout its length by a chamber 35 thru which water may be passed, in indirect heat transfer relation with the gas stream in Zone 35, by means of valve controlled inlet and outlet pipes 38 and 39. It will be understood that pipes 8 and 39 are connected with a suitable water cooling and circulating system, not shown, designed so as to effect flow thru cooling chamber 36 of whatever quantities of water may be needed to effect the desired cooling in Zone 35.

In practice, flow of water or other suitable medium thru chamber 36 is regulated so that the temperature of the gas stream exiting zone 35 at outlet 13| may be within the range of 25-45 C. and usually is around 30-40" C. At atmospheric pressure, anhydrous hydrogen fluoride gas condensed at about l920 C. and below. Since the condensation temperature is higher at the supersor 33, givenfcooling conditions in` preliminary.

condensing zone 35, and recycling of a. given quantity of anhydrous HF vapor as to be sub.-

sequently more fully describedfthe quantity of'4 HF which is condensed in the preliminary'coling zone 35 corresponds approximately with the make of the process. preliminary cooling zone 35 thru outlet '41, containing liqueed and unliquened HF aridvvhile.y still at the prevailing pressure,is`introduced into" a final cooling zone if? provided substantially,

throughout its length with a jacket 45 which forms a vaporizing chamber et, surrounding the gascooling zoned in indirect heat transfer relation.

'The cooling eiccted in zone Misl such as to cause liquefaction' of substantially all of the uncondensedHF. Cooling may be such as to reducetemperature ofthe gas stream and. contained to a "temperature substantially Ybelow the'cond'ensationfpoint,of'il-1F at the prevailing pressure; ei g. to'temperature ofY 5 C.-Zero C.v

or"bel ow. Inany case, temperature existing in tank 50 should b'e' lowfV enough underparticular conditions'j oifoperation as to minimize the amount ofV Hljvaponin the gasspace of the collecting tank."

In accordance Vwith the invention, the anhydrous liquid HF recovered 'in tankl is forced,

bythe vpressure y'existing' in the system,`thru pres-v sure reducing valve v5l and a pipef52 intctheu vaporizing zone li; In this zone, enough of the liquid HF'is vaporized ,in indirect heatv transfer relation with the residual gas mixture in final cooling zone 413 to effect the condensation there-v in "of residual uncondensed HF.A The amount of liquid'HFvaporized in zone 46 .depends upon th'e degreeof heatfremoval from thesystem in.

the preliminary cooling zone 35, the temperature` of the gas stream entering the inal' cooling zone' M and the amount of uncondensed Hlpresent.Y The vaporizing zone 46,' communicates thru pipe'- 55 with Apipe 3l 'andthe suction side of ,com-VV pressor 33.

Assuming agivenspeed of operation of lcorn-` pressor33, the amountofI vaporization of liquid` HF eiectedin zone Y125,' and'corresponding heat" I transfer from iinal cooling zone 44, may be regl-V ul'ated yby adjustment of valve v3l) in incoming, HF gas line 26 Thus, Aif the temperatureof the gas stream entering nal coolingzone 44 .and

the amount or unliqueedHF yare 'relatively ,higlpj valve 3U may-'be closedsufficiently to''prop'o1"` .,l tionately increase the amount of anhydrousHl".` vapor drawn intopipe 55 and correspondinglyf increase the amount 'of liquid HF .vaporized zone 45. Conversely, i1. the gas streamv introduced" j intonal coolingzone M is at relativelylov/"tema,

perature and' contains a smaller; amount of ,una liqueed HF, a smallerdegijeejof heatran'sfer in cooling zone44 is necessary, and the amount of vaporizationeffected in vapori'aing zone da` 3 'and 'correspondingly reducing the, amount of anhydrousV HF vapor draivn `thru pipe 55 back to 1 the'inletfside folcompressor 33 Thus`, as suming' a' givenl set of cooling conditions in` 'preliminary Th aSl Stream leaving,"

" with .ratiosv of V1:2 and 1:1,`respectively about 33% 7oV may be cut down asA required by opening valve zone 35, by simple adjustment of valve 30, depending upon the particular operating conditions at hand, the compression stage of the instant process may be so regulated as to eect vaporization of enough liquid HF in the vaporizing zone 46 to refrigerate the residual gas mixture suiiiciently to cause condensation of substantially all of the uncondensed HF-present in the nal cooling zone.

` It will be noted that the gas in compressor exit pipe 34 contains heat of compression, the sensible heat of the incoming HF gas, heat of vaporiz'ation ofA the HF in the incoming gas, plus whatever heat ofthe atmosphere may be transf Knitted inwardlyto the system, i. e. atmospheric heatdrawn. in thru the walls of the apparatus comprising the nal cooling stage, the collecting tank` 56 and associated pipe connections. In accordance with this invention, all the heat that is required to be abstracted from the system is removed bythe cooling*v water circulating thru chamber'35f By use of ordinary water coolingrv and circulating apparatusl it has been. found-to be readily possible .to removeall required heat frointhe process, and maintain temperature in the. exit gasl o f the preliminary cooling .operation at about 25-45". C. without -difculty The 4invention affords the marked. advantages that some of the sought-forv product itself lprovidesthennal refrigeration, and whatever heat must 'b e removed .from the systemmay be taken out ina commercially feasible way by simple` heat transfer to Water which need not be maintainedat temperatures lower than can be conveniently obtained: even .in .summer, bri-,readily operatedVV and ycontrolled Water cooling equipment. Forany given crude HF gas and overall design of zequipment, the process has only one major. point of operating control, namely, the quantity of waterwhich is circulated thru water coolinglchamber.. For any speciiic set of op-v erating'jconditions, the amount of anhydrous HF which is Avaporized. and recirculated4 thru the` compressor is relatively constant. Under most conditions met in practce, the volume ratio ofincomingl-IF gas to recirculated anhydrous HF vapormay varyfromsayfl to 1:4. Since as previously explained, the quantity of HF which is con`den`sed',.inthe prcliminarycooling Zone 35, corresponds approximately `with .the make` of theprocess',l when recycling HF'gas under conditions such' that the volume ratio of incoming HF gasto recirculated anhydrous HF vapor is about 1:4,Q abou t.20% weightof the total HF' present inzone.` 35,condenscslv Similarly, when Working and 501% by [Weight offthe vtOtalHF present in zone. 35 cond ense' s. In the more unusual but possiblefcircumstance infwhich the volume ratio,

on, in comingfHFgas to recirculatedanhydrous vapor is"abut. "1:l0. 5, approximately 66% byweight .ofv,the`tota l HF ,present in Zone, 35

iiquened. therein.l

vvThe Hfcontent of f the ,incoming gas,V constitutesjthe "make". ifI the process andisdrawn out latter'.l is ,maintained under atmospheric pressure,

and if .desired may be provided with insulation or offthe product.. .a` .temperature appreciably belowijthe boilingpointthereof.' Thus thel prof,

cefdure of .theinvention providesgror the manuof using extraneous refrigerating agent or requiring a nal fractionation step such as is used Widely in current operations.

The inert gas mixture collecting in the gas space in receiving tank 50` passes thru a reducing valve $2, and pressure is reduced to substantially atmospheric. The gas thus passes into the bottom of a tail gas clean-uptower 64 into the top of which cold strong e. g. 98-99% sulfuric acid is fed thru inlet 65. Preferably the tower is equipped with cooling coil 61 by which temperatures in the tower may be maintained low enough, e. g. C., to effect absorption by the sulfuric acid of any relatively small quantities of HF which may be entrained in the tail gas discharged from receiver 50. At temperatures of around Ztl- C. sulfuric acid absorbs HF and separates the same from any SiF4 and other inerts which may be in the gas stream. The effluent liquor of tower 64 may be run thru line 69 into the top of drying tower ll which, as previously stated, is operated at temperatures high enough to prevent absorption in the sulfuric acid of substantial amounts of HF. Thus, any HF which may be picked up in tail tower 64 is stripped out in tower Il and recirculated as a constituent of the incoming HF gas. All of the S03 which is brought into the process either as 98% sulfuric acid fed to tail tower 64 or as oleum introduced thru pipe 22 is eventually withdrawn from the system thru an outlet pipe 1I and may be utilized for decomposition of uorspar in furnace l0.

We claim:

1. The process for making substantially anhydrous hydrogen fluoride which comprises contacting crude HF furnace gas with strong sulfuric acid maintained at temperature above 90 C. and under conditions to dry said crude gas, and separating from the dried gas any entrained sulfuric acid mist to thereby form a gas mixture containing not less than 70% by weight of HF and not more than 0.5% by weight of H2O, introducing said gas mixture into a compression stage, compressing such gas mixture therein to substantial superatmospheric pressure whereby heat is developed in said gas mixture, removing heat from the compressed gas mixture in a cooling operation by indirect heat transfer to water under conditions to effect condensation of at least a substantial portion of the HF content of said compressed mixture, introducing the residual gas Y mixture containing residual uncondensed HF into a nal cooling stage, collecting liquid HF, vaporizing a portion of said liquid HSE' in indirect heat transfer relation with said residual gas mixture in said final stage, and recycling the thus vaporized HF with the incoming gas mixture at a point just ahead of said compression stage, regulating the volume ratio of incoming HF gas to recycled HF gas entering the compression stage to control the amount of HF thus vaporized and recycled thereby to refrigerate such residual gas mixture sufficiently to effect condensation in said final stage of substantially all of the residual uncondensed HF, regulating said water cooling operation so as to effect removal thereby of substantially all heat required to be extracted from the system, passing the tail gas of said final cooling stage into contact with strong cold sulfuric acid to absorb any HF contained in said tail gas, and then passing said sulfuric acid into said crude gas drying operation.

2. The process for making substantially anhydrous hydrogen fluoride which comprises introducing a purified HF furnace gas mixture containing not less than by weight of HF and not more than 0.5% by weight of H2O, into a compression stage, compressing such gas mixture therein to a pressure of not less than 20 lbs. gauge whereby heat is developed in said gas mixture, removing heat from the compressed gas mixture in a cooling operation by indirect heat transfer to water under conditions to effect condensation of at least a substantial portion of the HF content of said compressed mixture and to bring the temperature of the exit gas within the range of 25-45 C., introducing the residual gas mixture containing uncondensed HF into a nal cooling stage, collecting liquid HF, Vaporizing a portion of said liquid HF in indirect heat transfer relation with said residual gas mixture in said final stage and recycling the thus vaporized HF with the incoming gas mixture at a point just ahead of said compression stage, regulating the volume ratio of incoming HF gas to HF vaporized and recycled to a value in the range approximately 1:0.5 to approximately 1:4 thereby to control the amount of HF thus vaporized and recycled, said amount being sufficient to refrigerate such residual gas mixture sufficiently to effect condensation in said 11- nal stage of substantially all of the residual uncondensed HF and to bring the temperature of said HF condensate below about 5 C., regulating said Water cooling operation so as to effect removal thereby of substantially all heat required to be extracted from the system, and passing the tail gas of said final cooling stage into contact with strong cold sulfuric acid to absorb any HF contained in said tail gas.

EDWIN B. LOPKER. JOHN E. PEIRCE.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 1,266,621 Peterson May 21, 1918 1,530,461 Graham Mar. 17, 1925 2,351,461 Smith June 13, 1944 OTHER REFERENCES Handbook of Chemistry and Physics, 28th edition, pages 390-1 (1944), Chem. Rubber Publishing Co., Cleveland, Ohio. 

1. THE PROCESS FOR MAKING SUBSTANTIALLY ANHYDROUS HYDROGEN FLUORIDE WHICH COMPRISING CONTACTING CRUDE HF FURNACE GAS WITH STRONG SULFURIC ACID MAINTAINED AT TEMPERATURE ABOVE 90*C. AND UNDER CONDITIONED TO TRY SAID CRUDE GAS, AND SEPARATING FROM THE DRIED GAS ANY ENTRAINED SULFURIC ACID MIST TO THEREBY FORM A GAS MIXTURE CONTAINING NOT LESS THAN 70% BY WEIGHT OF HF AND NOT MORE THAN 0.5% BY WEIGHT OF H2O, INTRODUCING SAID GAS MIXTURE INTO A COMPRESSION STAGE, COMPRESSING SUCH GAS MIXTURE THEREIN TO SUBSTANTIAL SUPERATMOSPHERIC PRESSURE WHEREBY HEAT IS DEVELOPED IN SAID GAS MIXTURE, REMOVING HEAT FROM THE COMPRESSED GAS MIXTURE IN A COOLING OPERATION BY INDIRECT HEAT TRANSFER TO WATER UNDER CONDITIONS TO EFFECT CONDENSATION OF AT LEAST A SUBSTANTIAL TO EFFECT CONDENSATION OF AT LEAST A SUBSTANTIAL PORTION OF THE HF CONTENT OF SAID COMPRESSED MIXTURE, INTRODUCING THE RESIDUAL GAS MIXTURE CONTAINING RESIDUAL UNCONDENSED HF INTO A FINAL COOLING STAGE, COLLECTING LIQUID HF, VAPORIZING A PORTION OF SAID LIQUID HF IN INDIRECT HEAT TRANSFER RELATION WITH SAID RESIDUAL GAS MIXTURE IN SAID FINAL STAGE, AND RECYCLING THE THUS VAPOR- 